The invention relates to electric machines in general and more particularly to a cooling arrangement for the rotor of an electric machine, particularly a synchronous machine, which is provided with longitudinal slots each having a section of an exciter winding which is to be cooled to a low temperature disposed therein, the cooling arrangement having at least one coolant feed line and a discharge line.
The use of deeply cooled windings such as superconducting windings in electric machines permits a substantial increase of the induction in the air gap between the rotating machine part, e.g. the rotor, and the stationary machine part, e.g. the stator. Furthermore, higher current densities are obtained in windings with superconductors losses are practically eliminated. Therefore, the ratio of the power output to the volume and the weight is considerably higher in machines having superconducting exciter windings than in a machine of conventional design.
In U.S. Pat. No. 3,821,568 an a-c generator is disclosed which contains a rotor having an exciter winding which is cooled to a low temperature. The rotor is provided with longitudinal winding sections. These winding sections consist of a multiplicity of conductor layers arranged on top of each other in the radial direction and are subdivided in the circumferential direction into four conductor stacks insulated from each other (FIG. 3). Since these conductor stacks must be maintained at a low temperature, e.g. at helium temperature, if superconductor material is used for the conductors of the winding, they are partially wetted by a coolant. To accomplish this cavities through which the coolant is conducted are provided in a slot for each winding section. These cavities, which serve as cooling canals, permit the coolant to flow in the radial direction as well as in a direction parallel to the the axis of the rotor. At the bottom of the slot they are connected with chambers which serve as axial collecting canals for feeding and discharging the coolant. The coolant therefore rises from a collecting canal at the bottom of the slot radially to the cover of the slot at the two inner conductor stacks, then flows past the two outer conductor stacks and is fed to two further collecting canals at the slot bottom.
In this disclosed rotor, the coolant is fed in at the collecting canals at one rotor end and flows in the longitudinal direction of the rotor through the entire slot in planes along the conductor stacks. Since the coolant in the collecting canals on its way in is also in thermal contact, through metallic partitions, with the warmer coolant flowing in the return direction, excess temperatures can occur in this cooling arrangement for the rotor at the rotor parts facing away from the coolant inlet point. If superconductive material is used for the conductors of the winding a transition of the superconductors into the normal conducting state can therefore occur.